STOCKHOLM (Reuters) - Some countries have been "ambushed" by sudden severe outbreaks of disease and death from the H1N1 flu pandemic, and have gone over the top in their response, a European flu specialist said on Friday.

Angus Nicoll, influenza coordinator at the European Center for Disease Prevention and Control, said the apparent sudden surge of disease in Ukraine, which has reported at least 86 deaths from flu-like illness, was a feature of H1N1 -- which is mild in most people and can spread undetected for weeks.

"The mildness is good in some ways, but it has also given the disease control people some problems," Nicoll said.

"Then you get a Ukraine thing, where some countries have suddenly been ambushed by the pandemic and have gone over the top in their response."

Ukraine closed schools, banned public meetings including election rallies and restricted travel for three weeks from October 30 after it confirmed its first H1N1 death.

"The best bet is that this is actually a country that is 6 weeks into its pandemic," Nicoll told reporters at a briefing. "They just didn't notice it officially until young people started getting ill and going into hospital."

The epidemic coincides with the start of campaigning for a presidential election on January 17. and Prime Minister Yulia Tymoshenko, who announced the measures and is a front-runner in the election, said the outbreak would affect campaign rallies.

A team of experts from the Stokholm-based ECDC and the World health Organization in Geneva has gone to Ukraine at the request of its health ministry and are currently working in Kiev and Lviv, the ECDC said in an update on the outbreak.

It said it was "clear that pandemic H1N1.. has established itself in Ukraine" and it was likely that most of the rapidly spreading cases of respiratory disease were related to H1N1 flu.

Bitter political rivals in Ukraine are seeking to blame each other for poor handling of the H1N1 flu outbreak as the election approaches.

Nicoll said it was a "very complicated political situation" but said some of the steps taken to try to halt the spread of the disease were "very sensible": "They have reinforced hygiene, they have rapidly imported anti-virals, and...closing schools may have been a sensible thing to do."

He said it was the relative mildness in most people who catch H1N1 flu, which the WHO declared a pandemic in June and which has killed more than 5,700 people around the world, was one of the reasons Ukraine had apparently taken by surprise.

The virus is "not a big deal" for most people who get it, he said, while for others it is "very severe."